Palatinose-hydrolyzing Activity and Its Relation to Modulation of Flower Opening in Response to the Sugar in Dianthus Species

Abstract

Palatinose (isomaltulose) is an analog of sucrose and was regarded as non-metabolizable in plant tissues until recently. In the present study, we found that crude extracts from carnation petals had activity to hydrolyze palatinose. Preliminary characterization of this activity using a crude enzyme extract from ‘Lillian’ carnation petals revealed that hydrolyzing activity was exhibited by α-glucosidase, which uses isomaltose and palatinose, both being α-1,6-glucosides, as substrates. Exogenous application of palatinose stimulated flower opening of carnation cultivars (Dianthus caryophyllus ‘Lillian’, ‘Pure Red’, and ‘Light Pink Barbara’), but suppressed it in D. barbatus ‘Shin-higuruma’. Palatinose-hydrolyzing activity was much higher in the extract from carnation than that from D. barbatus. These observations suggested that palatinose stimulated flower opening in carnation by supplying glucose and fructose, but suppressed it in D. barbatus, probably through the inhibition of general metabolism, similar to the action of α-glucosidase, caused by its excess accumulation.